Current wireless access points (APs) allow for simultaneous operation in different bands (e.g., one in the 2.4 GHz band and one in the 5 GHz band). With the additional spectrum available in 5 GHz and the increasing bandwidth use of Wi-Fi based signals (up to 160 MHz bandwidth), many access point (AP) manufacturers want to add more 5 GHz radios into an AP. However, APs experience highly degraded performance when two co-located radios operate within the same band (e.g., two radios operating in the 5 GHz band). For example, when one radio transmits in close proximity to another radio that receives, packet reception is degraded by interference and throughput scaling is not achieved. Two factors that cause the interference include receiver overdrive and excessive transmitter noise floor.
Radio hardware is designed to operate over wide ranges of frequencies in a particular band (e.g., channels in the 5 GHz band). As such, receivers have gain and signal detection circuitry over the entire band. If one co-located and same-band radio transmits a high level signal, the high level signal can overdrive the other radio when it receives a desired signal due to close physical and spectral proximity of the radios. When this blocking occurs, the receiving radio typically loses any packets that it is currently decoding. This results in a loss of potential throughput and a “sharing” of the air time between the radios.
The second issue that limits the same band operation of co-located radios is excessive transmitter noise floor that exists in integrated circuits manufactured using currently available silicon processing technology. These integrated circuits and their associated hardware have limited outputs of band noise transmission using limited filtering capabilities which reduce baseband noise. This “transmitter noise floor” is apparent across the entire band of operation. This noise will appear in the band of the co-located same-band radio and limit the signal-to-noise-plus-interference-ratio (SINR) of that radio and in turn may limit the range of that radio. If this noise occurs during packet reception, it impacts the received signal's SINR greater than what that packet modulation would have accepted otherwise. As a result, in some circumstances, the received packet is lost.